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Risk Management Activities - Hedged items on the statement of financial position (Details) - CAD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of detailed information about hedging instruments [line items] |  |  |
Accumulated other comprehensive income | $ 302 | $ 454 |
Reserve of exchange differences on translation |  |  |
Disclosure of detailed information about hedging instruments [line items] |  |  |
Accumulated other comprehensive income | (21) | (21) | $ 17
Physical power sales | Cash flow hedges | Commodity risk management |  |  |
Disclosure of detailed information about hedging instruments [line items] |  |  |
Gain (loss) on hedge ineffectiveness | (33) | 47 |
Reserve of cash flow hedges | 417 | 527 |
Interest Expense On Long-Term Debt | Cash flow hedges | Interest rate risk |  |  |
Disclosure of detailed information about hedging instruments [line items] |  |  |
Gain (loss) on hedge ineffectiveness | 7 | 0 |
Reserve of cash flow hedges | 19 | 0 |
Foreign-denominated debt | Net Investment Hedge | Currency risk |  |  |
Disclosure of detailed information about hedging instruments [line items] |  |  |
Gain (loss) on hedge ineffectiveness | $ 11 | $ 21 |

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- Definition The amount of accumulated items of income and expense (including reclassification adjustments) that are not recognised in profit or loss as required or permitted by other IFRSs. [Refer: IFRSs [member]; Other comprehensive income] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_55&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The gain (loss) on hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 24C -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_24C_a_i&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition A component of equity representing the accumulated portion of gain (loss) on a hedging instrument that is determined to be an effective hedge for cash flow hedges. [Refer: Cash flow hedges [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 78 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_78_e&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 9 -IssueDate 2019-01-01 -Paragraph 6.5.11 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=9&code=ifrs-tx-2019-en-r&anchor=para_6.5.11&doctype=Standard -URIDate 2019-03-27 + Details
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